The County of Frontenac was originally proclaimed in 1792, as part of the newly-created Midland District. The County of Frontenac was joined by neighboring Lennox and Addington counties as one of the original 19 counties in Upper Canada, which would later become Ontario.
Small communities such as Simcoe Island, Howe Island, Garden Island, as well as several others, were mostly settled due to their easy accessibility by boat from both Canada and the United States.
On January 1, 1998, the 18 former townships were restructured to form four – the Townships of North, Central and South Frontenac and the Frontenac Islands, represented by their respective mayors on a four-member County Council.